Bert says that a charged particle in a vacuum can travel in a helix only if a uniform electric field and a uniform magnetic field are both present and both parallel to the axis of the helix. Stuart says that only a magnetic field with a component parallel to the axis of the helix is needed. Which one, if either, is correct, and why?
a. Bert, because the charged particle's velocity can have a vertical component only if an electric field in the vertical direction is present.
b. Stuart, because a component of velocity in the vertical direction is not changed by a vertical component of a magnetic field.
c. Bert, because a component of velocity in the vertical direction is changed by a vertical component of a magnetic field.
d. Stuart, because an electric field in the vertical direction would cause the particle to come to a complete stop.
e. Neither, because particles cannot move in helical paths in the presence of magnetic and electric fields.
b
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Ariel claims that a pulse is described by the equation 
where x and y are measured in cm and t in s. Miranda says that it is not possible to represent a pulse with this function because a wave must be a function of x + vt or x?vt. Which one, if either, is correct, and why?
A.
B.
C.
D.
E.
is infinite when x = 0.A gas-filled vertical cylinder, closed at the bottom end, is fitted at the top with a piston that can move freely. The mass of the piston is 10.0 kg,
and the initial height of the piston above the bottom of the cylinder is 25 cm. A mass of 8.0 kg is placed on the piston. What is the resulting height of the piston, assuming that the temperature of the ideal gas is kept constant? A) 12 cm B) 13 cm C) 14 cm D) 15 cm E) 16 cm
When Earth is nearest the Sun, the Northern Hemisphere is experiencing
a) autumn. b) spring. c) summer. d) winter.